Derwent Estuary, Tasmania

Named after the Celtic word 'clear water' in 1794 the Derwent estuary population has since grown substantially and now boasts 40% of Tasmania's population along its periphery. The estuary is an important and productive area with a variety of habitats including areas of wetlands, intertidal flats, kelp beds, seagrasses and rocky reefs that support a wide range of species, including black swans, oyster catchers, migratory bird species, penguins, dolphins and seals, platypus and seadragons. The critically endangered Spotted handfish, Brachionichthys hirsutus, is endemic to south-eastern Tasmania and occurs in few places, one being in the coarse sand habitats of the lower Derwent River estuary.

As with many estuaries, local population growth has occurred resulting in estuary waters being used more and more for recreation, industry and marine transport. The upstream Derwent river provides the majority of the regions drinking water and is a source of energy via hydroelectric power stations. However these activities take their toll. Sedimentation has increased, there is heavy metal contamination, sewage problems, which together have lowered the oxygen level is some areas as nutrients have increased. Scallop dredging has destroyed seagrass and kelp beds, and kelp has been overharvested. It has been reported that approximately 400 ha of seagrass beds have disappeared from Ralphs Bay during the past 50 years, and large wetland areas in the upper estuary have also suffered recent degradation (e.g. Murphys Flat).

There have been some improvements in the water quality in the Derwent over the past 10 years, as a result of reduced end-of-pipe emissions from sewage treatment plants and local industries.